Mechanism of surface reaction in the deposition process of a-Si:H by rf glow discharge.

Abstract

Hydrogenated amorphous Si (a-Si:H) films are deposited by the rf glow discharge of ${\mathrm{SiH}}_{4}$. The mechanism of the surface reaction of the incident ${\mathrm{SiH}}_{3}$ radical produced by the glow discharge to form the a-Si:H network was studied in this work. The hydrogen concentration was investigated by IR absorption in a-Si:H films deposited under various conditions of the substrate temperature ${\mathit{T}}_{\mathit{s}}$ and the ${\mathrm{SiH}}_{4}$ partial pressure ${\mathit{P}}_{\mathit{s}}$ in the reactant gases. The hydrogen concentration in the films was divided into SiH and ${\mathrm{SiH}}_{2}$ configurations by spectral deconvolution. While the SiH concentration ${\mathit{S}}_{1}$ was not influenced very much by variation of the deposition conditions, the ${\mathrm{SiH}}_{2}$ concentration ${\mathit{S}}_{2}$ was remarkably influenced. ${\mathit{S}}_{2}$ increased with an increase in the deposition rate of the film at a different rate by the variation of ${\mathit{T}}_{\mathit{s}}$ and ${\mathit{P}}_{\mathit{s}}$. The following reaction scheme of the radicals adsorbed on the growing surface is proposed to explain these changes in ${\mathit{S}}_{2}$ and ${\mathit{S}}_{1}$. The dehydrogenation and Si-Si bond formation into the network are made by two kinds of processes, the fast process and the slow process. The fast process occurs predominantly in high-rate depositions and incorporates ${\mathrm{SiH}}_{2}$ into the network. The slow process occurs predominantly in low-rate depositions and incorporates some SiH. The fast process takes place by interactions of two adsorbed radicals and the slow process takes place at steplike sites after migration on the surface.